Filament structure



April 30, 1957 J. w. SKEHAN FILAMENT STRUCTURE Filed July 28, 1955 F l G 2 mvENTOR z z 1 I I I 1 JOSEPH W. S EHAN u m. 6 2 9 m 8 3 ATTORN United States atent FILAMENT STRUCTURE Joseph W. Skehan, Stamford, Conn., assignor to Machlett Laboratories, Incorporated, Springdale, Conn., a corporation of Connecticut Application July 28, 1953, Serial No. 370,674

6 Claims. (Cl. 313-273) This invention relates to filament structures for use in electron tubes, particularly in high power electron tubes. In particular, this application relates to a simple, sturdy, filament structure which employs a simple support s-truc ture.

In modern tube applications it is desirable to provide filament structures which will provide maximum efficiency with minimum power loss. It is particularly desirable to obtain a high power output without having to dispose of a great deal of heat generated by lost power. To this end, filaments have been constructed of various high emission materials, such as thoriated tungsten, which ice that the helical portions will remain in their proper orientation. Rigidization of this non-emissive portion by reinforcing means causes it to maintain its diametric position and remain essentially straight except under conditions of shock. The means of the reinforcement may vary, but it is usually most convenient to wrap the prorequire relatively low currents to attain a desired amount handling, electron tubes are subjected to mechanical shock. When a strand of fragile or brittle material is mounted between a pair of relatively solid support members, it is unable to yield in such a manner as to absorb the shock, and the brittle strand will break.

The present invention provides a novel filament structure which is capable of absorbing mechanical shock A structure having unlimited free- Without breakage. dom to absorb shock would be undesirable because it would probably also have the ability to change shape and possibly to short to the adjacent electrode. structure, while capable of considerable flexibility under shock, will retain its specific shape under all the shock This novel conditions that are usually encountered. This shape is such as to permit accuracy in interelectrode spacing over The present structure involves solid mounting for the filament strandf at one end and resilient mounting at the opposite end of the active filament portion. While the structure is quite the length of the active filament portions.

rugged and'able to absorb shock normally encountered in shipping and handling, it is also extremely simple and The emissive portions of the filament are helical in shape and are coaxially arranged to conform to the contour of the adjacent cylindrical electrode. Across a diameter at one end of the cylindrical surface defined by these helical emissive filament portions extends a connecting or intermediate portion of the filament. This connecting portion is rigidized in such a manner that it will normally remain essentially straight and extend across the diameter of the cylinder but so that it will readily yield under shock. Usually this rigidization will cause an increase in the effective diameter of the non-emissive filament portion. Accordingly, this connecting portion may be considered essentially non-emissive because of 1ts greater effective diameter, hence lower resistance and less tendency to become heated, than the ennss1ve portions. It is important that this non-emissive portion be ma ntained in its position as a diameter of the cylinder so posed non-emissive portion of the filament with heavy wire, thereby forming a helical covering or sheath over the filament in the regionvwhich is to be non-emissive. Because of the resulting relative rigidity of this non-emissive portion, one solid support member then becomes sufiicient to hold the whole non-emissive filament portion.

This solid support is preferably furnished by an axial rod which is afiixed to the reinforced non-emissive filament portion. The ends of the filament strand are terminated at the opposite ends of the cylinder defined by the filament portion. Each of these ends of the filament may be mounted on a solid support. These support members for the ends of the filament may be of any conventional type which permits the active filament strand to remain in posit-ion on the cylindrical surface which it defines.

For a better understanding of this invention reference is made to the accompanying drawings which maybe generally described as follows:

Fig. 1 illustrates, in partial section taken along line 11 in Fig. 2, an electron tube diode employing my novel filament, which filament is shown in elevation;

Fig. 2 is a cross-sectional view of the tube shown in Fig. 1 taken along the line 22 in Fig. 1;

Fig. 3 is a detailed view of the supporting member for the non-emissive portion of my novel filament;

Fig. 4 illustrates modified means supporting and rigidizing the filaments essentially non-emissive portion.

Referring to the drawings, it may be seen that the present invention may be employed in an electron tube structure having a generally cylindrical vacuum envelope 10 advantageously composed of glass. At its opposite ends the diameter of the cylindrical envelope may be reduced to form neck portions 11 and 12, respectively. The end of the envelope at neck portion 11 is terminated in a reentrant envelope portion 13 which itself is terminated in stem press 14. Similarly, neck portion 12 is closed by reentrant envelope portion 15 which terminates in stem press 16.

A generally cup-shaped anode 18 providing a cylindrical active surface internal of the cup is supported on the stem press 14. Actual support is furnished by rodlike member 19 which is embedded in stem press 14 and connected by annular flange member 19a, or similar means, to the bottom of anode cup 18. Supporting rod 19 penetrates the vacuum envelope through press 14 and is affixed externally of the vacuum envelope to a flexible lead 21.

The filament structure consists of strand portions, which are preferably a single strand, as illustrated, apportioned into emissive and non-emissive portions of the filament. The emissive portions 23 and 24 are helical in form and preferably extend over They may extend over any selected angle, however. These helical portions are arranged coaxially in the tube to define a cylindrical surface which is coaxial with anode 18. The non-emissive filament portion 25 extends generally diametrically across one end of the cylinder and joins the two helical portions 23 and 24. Solid mounting is provided for the ends of the filament strand by tabs 26 and 27 which are connected respectively to rods 28'and 29. As illustrated, rods 28 and 29 penetrate the vacuum envelope through press 16- and maybe terminated respectively in flexible leads 30-and. 31. Solid support for the other position of the filament;

resistance and because'as the filament strand shifts within such tabsduring use,- the overall, resistance of the fila-- ment structure is changed.- Accordingly, elimination of two such tabs bothreduces filament resistance and makes said resistance more stable. At the sametime elimination ,of some of the tabs simplifies the filament structure and makes itless costly to manufacture.

Axial .rod 33 is advantageously terminated. in an eye 33a through which: passes ,filamentportiQnlS, as may bescenrtin.greatendetailinfig, 3. .A-rigidizing covering,34.extends over much of the non-emissive portion ZS-of the..fila.ment. This rigizidingpovering advantageouslyfconsists .of a helical Winding of --refractory.metal wire of sufficient wire diameter/and sufiicient helical pitch to normally insure-relatively fixed position of this non-emissive portion .of the filament. Thisrigidizing means must, ,however, even, at high temperatures, permit a minimum of flexibility which is suflicient to absorb shocks lto which the-filament is subjected, andat the same time-a maximum of rigidity which will serve to prevent changes in shape of ,the supportedemissive portions of the filament. A clip-likeshield 36 is placed over the end of rod. 33 to reinforce its relatively fragile eye portion 33a.

It is advantageous to employ shieldingmeans at the filament end of the tube. Shielding means 38 is mounted upon axial rod 33 in some conventional manner, as by annular bracketf39, and arranged about stem press 16 to protect said pressfrom high voltage effects, particularly from random particles. Care must be taken to prevent shield 38 from making contact with rod connections--28 and 29, and, accordingly, theholes inshield 38, through which said rods pass, are considerablyenlarged.

As has been previously mentioned, this filament structure is particularly valuable for use with thon'ated tungsten filaments. When thoriated tungsten filaments are employed, the highdegree of vacuum required to we vent the poisoning of the thoriated filament may necessitate the use of getters within the tube envelope to clean up residual gases and to maintain a high degree ofvacuum at all times. Any of the wellknown getter substances and gettering structures which are satisfactory for use with thoriated' tungsten, filaments may be employed with this novel filament structure.

' When a thoriated tungsten filament is employed, high emission density is obtained because of the. action of a tungsten carbide sheath forming the outer layer of the filament. In order to provide this carbide sheath, the thoriated tungsten filament is heated to 'a prescribed temperature for a prescribed period in-acarbonaceous atmosphere. In the manufacture of the filament of the present invention, the thoriated tungsten filament-is not placed:in-acarbonaceous atmosphere for activation until his fullyassembled. Preferably it is not carburized until it is mounted on oneendof the-tubeienvelope structure which is readygto be sealed to thexrest of: the.

tube envelope structure which mounts theOther-tube' electrode. As the filament is heatedwin' a carbonaceous atmosphere, the diametric portion of-the, filament does supporting enter mast. nd anot er, typ of 'sidiains means for the non-emissive portion of the filament. In this instance, the casing 34 is engaged by hook member 33a which terminates rod member 33'.

Many other modifications of the support and rigidizing means for the filament are possible. For instance, a tubular metallic member might be employed in place of the helical windingor braided covering. Many other means of rigidizing and supporting the non-emissive portion of the filament will occur to one skilled in the art and are capable of being substituted for the structures illustrated.

Although this. inventionis particularly valuable for use with thoriated tungsten filaments because of its ability to absorb shock and yet retain its shape and position, the present invention is valuable for use with other filament materials, too. Other variations in the structure shown and described are possible. For example, the filament strand may becomposed of two strands in series rather than one, and more than one filament structure may be employed in a tube. Various other modifications in the structures shown and described will occur to those skilled in the art ,and are intended .to be within the-scope and spirit of this invention.

Iclaim:

1. A filament structure for use-in electron tubes havingacylindrical electrode geometry,,said filament-structure=comprising a filamentary strand having two emissive portions and an intermediate portion which is essentially non-emissive, said 'emissive portions being. essentially helical inform and defining a cylindrical surface and said relatively non-emissive portion being of predetermined shape and diametrically crossing one end of the cylinder defined by the emissive portions, shape maintaining means securedto the non-emissive portion of said filament in order to maintain it in substantially its initial shape, support means aflixed to the non-emissive reinforced portion, and separate support means at the ends of the filament strand at the oppositeend of the cylinder from the reinforced filament portion and on the same general axial level with one another.

2. A filament structure for usewithin ,an'electron tube having a cylindricalelectrode geometry, said structure comprising stranded filament means which is apportioned into two emissive portions of essentially helical form defining a cylindrical surface and a non-emissive portion; intermediate saidemissive portions and generally diametrically mounted across one endof the cylinder definedby the emissive filament portions, means maiutainingthe diametrically mounted portion in substantially. its initial shape, rod-,like-support, means afiixed to the non-emissive filament portion andsupport means at the ends of-the stranded means atthe-opposite end;of the cylinder defined by said filament from 'the-non-cmissive filament portion.

3. A rectifier tube having within a vacuum envelope a cylindrical anode land-1a" filament structure having :active emissive portions defining a cylinder coaxially mounted within said anode, said filament structure comprising a single; filament strand having three portions, the two portions adjacent the endof said strand being essentially helical andbeing theemissive filament portions defining ,the cylinder and the intermediate non-emissive portion of the filament generally defining adiameter of the, cylinder at one end thereof; a rigidizingwrapping consisting-of wire helically wound around the non-emissive .portionof the filament, an-axial -support;rod'afiixed to thenon-emissive portion, and'a pair of support memhers at the-rrcspective ends of-the=filament strand at the opposite end ofithe cylinder from thenon-ernissive portion.'

4. 'A filament'structure for use within-an electrontube having a cylindrical electrode geometry, said structure comprising stranded filament means which isappo rtionedinto two emissive portions of essentially helical form defining a cylindrical surface and a non-emissive portion intermediate said portions and generally diametrically mounted across one end of the cylinder defined by the emissive filament portions, a winding of wire arranged helically around said non-emissive portion for reinforcement, rod-like support means affixed to this non-emissive filament portion and support means at the ends of these stranded means at the opposite end of the cylinder defined by said filament from the non-emissive filament portion.

5. A filament structure for use within an electron tube having a cylindrical electrode geometry, said structure comprising stranded filament means which is apportioned into two emissive portions of essentially helical form defining a cylindrical surface and a non-emissive portion intermediate said emissive portions and generally diametrically mounted across one end of the cylinder defined by the emissive filament portion, a winding of wire arranged helically around said non-emissive portion for reinforcing this diametrically mounted portion, an axial rod support engaging the non-emissive filament portion at one end and support means at the ends of the stranded means at the opposite end of the cylinder defined by said filament from the non-emissive filament portion, said support means and axial rod support being supported on the vacuum envelope.

6. A filament structure comprising a filament strand having two opposed emissive helical portions joined at one end by an integral non-emissive interconnecting portion, said helical portions having been carburized and said integral non-emissive interconnecting portion remaining uncarburized, and means making electrical connection to the emissive helical portions at the ends thereof opposite those joined by said integral interconnecting portion.

References Cited ,in the file of this patent UNITED STATES PATENTS 708,432 Webster Sept. 2, 1902 1,884,957 Adams Oct. 25, 1932 1,928,202 Meyer et al. Sept. 26, 1933 1,936,762 Howe Nov. 28, 1933 2,397,854 Glauber Apr. 2, 1946 2,414,501 Wheeler Jan. 21, 1947 2,442,141 Skehan June 10, 1947 

